1. Technical Field
The present invention relates to a thin film transistor (“TFT”) substrate and a method of manufacturing the same and, more particularly, to a TFT that can directly contact indium tin oxide (“ITO”) or indium zinc oxide (“IZO”) and has desirable voltage-current characteristics, a TFT substrate including the TFTs, and a method of manufacturing the same.
2. Discussion of the Related Art
A TFT substrate is used as a circuit substrate for driving respective pixels in a flat panel display device such as a liquid crystal display (“LCD”) device, an organic light emitting diode (“OLED”) display device, and the like. The TFT substrate includes a TFT arranged in each pixel area, and a pixel electrode connected to the TFT.
The gate lines and data lines carry signals to drive the TFTs using a voltage applied from an external driving circuit. Ends of the gate lines and data lines are exposed to be coupled to a driving circuit and then connected to a separate contact electrode to protect the exposed portions. The contact electrodes are formed of a transparent conductive material such as ITO, IZO, etc. The gate lines and data lines should be formed of a material having low contact resistance for the purpose of the connection with the contact electrodes.
Accordingly, conventional gate and data lines are formed of an alloy containing aluminum (Al), or a single metal such as AlNd, Cr, Mo, Cu, etc., in a single or multi-layer structure. Since internal resistance is considered, the gate lines are formed in a multi-layer structure of Al/AlNd, AlNd/Mo, Al/AlNd/Cr (or Mo), etc., and the data lines are formed in the same structure as the gate lines or in a multi-layer structure of Al/Mo, Mo/Cr/Mo, etc. When the gate lines and data lines are formed in such a multi-layer structure, it is necessary to add a process of stacking metals and to further use etchants for etching respective metals in an etching process, thus increasing process and material costs.
Furthermore, when exposing the gate line and data line for the purpose of the connection with the contact electrodes, the metals on the lower part of an insulating layer are overetched according to different etching ratios of the stacked metals to cause a void, thus resulting in corrosion on the metals due to penetration of the etchants during the formation of the contact electrodes.
In addition, if a metal containing aluminum (Al) is used as source and drain electrodes between an ohmic contact layer and source/drain electrodes during the formation of the TFT, the Al component may be diffused into the ohmic contact layer due to high temperature generated during the formation of a protection layer and a pixel electrode in the subsequent process, thus deteriorating the TFT characteristics.